1. Field of the Invention
The present invention relates to a method for producing phosphorus-containing polymers, and more particularly, the present invention relates to a method for producing phosphorus-containing polymers possessing excellent acid resistance and alkali hydrolysis resistance.
2. Description of the Prior Art
It is known that phosphorus-, nitrogen-, and halogen-containing compounds are generally effective in imparting flameproofness to cellulose fibers. However, since these flameproofing chemicals are usually added to the fibers by impregnation in the step of after-treatment of the fibers, the hand feel quality and mechanical characteristics of the fibers are significantly damaged. Moreover, it is difficult by the conventional procedure to obtain fibers which maintain their flameproof characteristics after repeated washings.
Recently, in an attempt to improve this detrimental characteristic, several methods have been proposed for producing flameproof fibers which exhibit improved washing fastness by incorporating a flameproofing agent into a viscose and then wet spinning the viscose to disperse the flameproofing agent in the fibers. The flameproofing agents which are typically mixed with viscose, include various known phosphate compounds, phosphonitrile compounds, and the like. However, when the phosphate compounds are used, the fibers exhibit poor resistance to laundering, coloration of the fibers, and hydrolysis of the phosphate compounds with alkali present in the viscose.
The phosphonitrile compounds characteristically impart good flameproofness to the fibers, but they are very expensive. Furthermore, the fibers also possess poor resistance to laundering and do not retain much of the flameproofing agent. Also, the flameproofing agent oozes out of the fibers.
Recently, methods which use phosphorus-containing compounds have been proposed to solve these problems. For example, U.S. Pat. No. 3,371,131 shows that a phosphonate polymer obtained by the reaction of a ketone and cyclic chlorophosphite compound is effective as a flameproofing agent.
In fact, there are a number of methods which involve the production of similar phosphonate polymers followed by mixing the polymers with viscose and then spinning the viscose into a coagulation bath. These methods are disclosed in Japanese Pat. Publication No. 2693/73 and Japanese Pat. Laid-open Nos. 23612/72, 42125/73, 44519/73, 75816/73, 91312/73, 99417/73, 102200/73, 25218/74 and 35613/74. According to these methods, the deficiencies of the known flameproofing methods are improved, but these phosphonate polymers have the detrimental characteristic that they are partially hydrolyzed by alkali in the viscose.
A need, therefore, continues to exist for a method of improving the various mechanical and physical properties of fibers containing flameproofing agents.